The present invention relates to a silver halide photographic light-sensitive material. In particular, the present invention relates to an ultrahigh contrast negative type photographic light-sensitive material suitable as a silver halide photographic light-sensitive material used for a photomechanical process.
In photomechanical processes used in the field of graphic arts, used is a method in which photographic images of continuous tone are converted into so-called dot images in which variable image density is represented by sizes of dot areas, and such images are combined with photographed images of characters or line originals to produce printing plates. For silver halide photographic light-sensitive materials used for such a purpose, ultrahigh contrast photographic characteristic enabling clear distinction between image portions and non-image portions has been required in order to obtain favorable reproducibility of characters, line originals and dot images.
As a system responding to such a requirement, there has been known the so-called lithographic development method in which a silver halide light-sensitive material comprising silver chlorobromide is treated with a hydroquinone developer having an extremely low effective concentration of sulfite ions to obtain images of high contrast. However, in this method, the developer is extremely unstable against oxidation by air since the sulfite ion concentration in the developer is extremely low, and therefore a lot of developer must be replenished in order to stably maintain the developer activity.
As image forming systems in which the instability of the image formation according to the lithographic development method is eliminated and light-sensitive materials are processed with a developer showing good storage stability to obtain ultrahigh contrast photographic characteristic, there can be mentioned those described in U.S. Pat. Nos. 4,166,742, 4,168,977, 4,221,857, 4,224,401, 4,243,739, 4,269,922, 4,272,606, 4,311,781, 4,332,878, 4,618,574, 4,634,661, 4,681,836, 5,650,746 and so forth. These are systems in which a silver halide photographic light-sensitive material of surface latent image type containing a hydrazine derivative is processed with a developer containing hydropuinone/metol or hydroquinone/phenidone as main developing agents and 0.15 mol/l or more of sulfite preservative and having pH of 11.0-12.3 to form ultrahigh contrast negative images having a gamma of 10 or higher. According to these systems, photographic characteristics of ultrahigh contrast and high sensitivity can be obtained, and because sulfite can be added to the developer at a high concentration, stability of the developer to air oxidation is markedly improved compared with conventional lithographic developers.
In order to form sufficiently ultrahigh contrast images with use of a hydrazine derivative, it is necessary to perform processing with a developer having pH of 11 or higher, usually 11.5 or higher. Although it becomes possible to increase the stability of the developer by use of a sulfite preservative at a high concentration, it is necessary to use such a developer of high pH as described above in order to obtain ultrahigh contrast photographic images, and the developer is likely to suffer from air oxidation and instable even with the presence of the preservative. Therefore, various attempts have been made in order to realize ultrahigh images with a lower pH to further improve stability of the developer.
For example, U.S. Pat. No. 4,269,929 (Japanese Patent Laid-open Publication (Kokai, henceforth referred to as xe2x80x9cJP-Axe2x80x9d) No. 61-267759), 4,737,452 (JP-A-60-179734), 5,104,769, 4,798,780, JP-A-1-179939, JP-A-1-179940, U.S. Pat. Nos. 4,998,604, 4,994,365 and JP-A-8-272023 disclose methods of using a highly active hydrazine derivative and a nucleation accelerator in order to obtain ultrahigh images by using a developer having pH of less than 11.0.
However, since silver halide photographic light-sensitive materials used for such image-forming systems contain highly active compounds, they suffer from problems concerning storage stability such as fluctuation of sensitivity and increase of fog during storage. Most of the problems are caused due to high emulsion sensitivity, and therefore it has been desired to develop a technique for obtaining higher sensitivity with superior storage stability.
Considering these problems of the conventional techniques, an object of the present invention is to provide a silver halide photographic light-sensitive material that provides high contrast and high sensitivity.
As a result of various researches of the inventors of the present invention, they found that the aforementioned object could be achieved by a silver halide photographic light-sensitive material containing a compound of a particular structure and having a particular gamma, and accomplished the present invention.
That is, the present invention provides a silver halide photographic light-sensitive material comprising at least one silver halide emulsion layer on a support, which contains at least one compound selected from compounds of the following Types (i) to (iv) and has a characteristic curve drawn in orthogonal coordinates of logarithm of light exposure (x-axis) and optical density (y-axis) using equal unit lengths for the both axes, on which gamma is 5.0 or more for the optical density range of 0.3-3.0.
Type (i)
A compound of which one-electron oxidized derivative produced by one electron oxidation of the compound is capable of releasing two or more electrons with a bond cleavage.
Type (ii)
A compound of which one-electron oxidized derivative produced by one electron oxidation of the compound is capable of releasing one more electron with a carbon-carbon bond cleavage and which has two or more groups adsorptive to silver halide in the same molecule.
Type (iii)
A compound of which one-electron oxidized derivative produced by one electron oxidation of the compound is capable of releasing one or more electrons after undergoing a bond formation reaction.
Type (iv)
A compound of which one-electron oxidized derivative produced by one electron oxidation of the compound is capable of releasing one or more electrons after undergoing an intramolecular ring cleavage.
In the present invention, the compounds of Types (i) to (iv) are preferably compounds represented by following formulas (1-1) to (4-2). 
In the formula (1-1), RED11 represents a reducing group, L11 represents a leaving group, and R112 represents a hydrogen atom or a substituent. R111 represents a nonmetallic group that can form a ring structure corresponding to a tetrahydro, hexahydro or octahydro derivative of a 5- or 6-membered aromatic ring (including an aromatic heterocyclic ring) together with a carbon atom (C) and RED11.
In the formula (1-2), RED12 and L12 each represent groups having the same meanings as the groups RED11 and L11 in the formula (1-1) respectively. R121 and R122 each independently represent a hydrogen atom or a substituent. ED12 represents an electron donor group. R121 and RED12, R121 and R122 or ED12 and RED12 may bond to each other to form a ring structure.
In the formula (2), RED2 represents a group having the same meaning as RED12 in the formula (1-2). L2 represents a carboxyl group or a salt thereof, and R21 and R22 each independently represent a hydrogen atom or a substituent. RED2 and R21 may bond to each other to form a ring structure. However, the compounds represented by the formula (2) are compounds having two or more groups adsorptive to silver halide in each molecule.
In the formula (3), RED3 represents a group having the same meaning as RED12 in the formula (1-2). Y3 represents a reactive group containing a carbon-carbon double bond site or carbon-carbon triple bond site that can react with one electron oxidized derivative produced by one electron oxidization of RED3 to form a novel bond. L3 represents a bridging group bonding RED3 and Y3.
In the formulas (4-1) and (4-2), RED41 and RED42 each independently represent a group having the same meaning as RED12 in the formula (1-2). R40 to R44 and R45 to R49 each independently represent a hydrogen atom or a substituent. In the formula (4-2), Z42 represents xe2x80x94CR420R421xe2x80x94, xe2x80x94NR423xe2x80x94 or xe2x80x94Oxe2x80x94. R420 and R421 each independently represent a hydrogen atom or a substituent, and R423 represents a hydrogen atom, an alkyl group, an aryl group, or a heterocyclic group.
Among the aforementioned compounds of Type (i), Type (iii) and Type (iv), more preferred are those compounds having a group adsorptive to silver halide and/or a partial structure of sensitizing dye in the molecules. Still more preferred are those having a group adsorptive to silver halide in the molecules.
The silver halide photographic light-sensitive material of the present invention preferably contains a hydrazine compound. Further, it preferably has a film surface pH of 6.0 or less, more preferably 4.5-6.0, on the emulsion layer side.
According to the present invention, there can be provided a high contrast silver halide photographic light-sensitive material that shows high sensitivity and good storage stability. The silver halide photographic light-sensitive material of the present invention is useful as an ultrahigh contrast negative type photographic light-sensitive material suitable as a silver halide photographic light-sensitive material used for a photomechanical process.